The present invention relates to a hydraulic piston-valve-type control valve that includes a housing in which a control piston is longitudinally displaceably disposed. By means of annular recesses, and hence control surfaces that are formed on piston collars about piston cores, the control piston regulates at least one fluid stream that flows through the housing. Regulation is effected by coupling the recesses between the piston collars with annular control spaces on the housing side via appropriate longitudinal displacement of the control piston. The piston collars are provided with control edges that progressively release or open the control spaces or chambers.
Control valves of this general type are known from German Pat. No. 27 17 384 and German Offenlegungschrift No. 32 05 860. Both control valves are so-called continuous or step slide valves that provide a fine controllability of the valve by providing the control edges with triangular recesses which, relative to the cross section of the control surfaces, generally have the three-dimensional shape of a half cone. With such piston geometries, during the opening stroke or movement of the valve piston, the control edges of the latter, beginning from the tip of the triangular recess, progressively release the control spaces or chambers disposed in the housing annularly about the piston. As a result, where smaller current flows are involved, it is possible to have a fine control of the valve with the desired precision. Furthermore, the known course for the control edges is suppose to prevent a breakdown or turbulence of the fluid flow at the control edges, as occurs with linear control edges that cooperate with the control chambers in the so-called neutral section. Inherent to such a breakdown of the fluid flow is a force imbalance in the direction of flow of the medium. In contrast to the desired fine control, such an imbalance tends to force the opening movement of the piston forward in an abrupt manner.
The drawback of providing the configuration of the control edges as triangular recesses, i.e. of providing the control surfaces as semi-conical recesses, is that although in the triangular region of the control edges it is possible to realize a fine control of the valve, when the control piston is extended out of this region, and when the full open position is achieved, the volume flow of the medium is increased in an abrupt manner, resulting in the undesired sudden increase of the flow forces. Another drawback of the known configuration of the control edges is that such a configuration is expensive to manufacture. Above all, the known configuration for the control edges or recesses, requires considerable milling effort relative to the control surfaces since the opening stroke characteristic of the control valve depends to a critical extent upon the precision of the configuration of the control edges or control surfaces. Since the piston is a hardened component, the hardening process that follows milling of the course of the control edges or control surfaces again conveys imprecision related to this hardening process into the workpiece.
It is an object of the present invention to improve a valve of the aforementioned general type in such a way that while providing good fine controllability of the valve, sudden movements of the flow forces are avoided. At the same time, the valve, and in particular the piston thereof, should be easier to manufacture in a more precise manner.